1. What is the Duct Design Equation?

The duct design equation calculates the required cross-sectional area of an HVAC duct based on airflow (CFM) and desired air velocity. Proper duct sizing is essential for efficient HVAC system operation.

2. How Does the Calculator Work?

The calculator uses the duct area equation:

Where:

• \( A \) — Duct cross-sectional area (square feet)
• \( CFM \) — Airflow in cubic feet per minute
• \( V \) — Air velocity in feet per minute

Explanation: The equation balances airflow requirements with velocity constraints to determine optimal duct size.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures proper airflow, minimizes energy consumption, reduces noise, and maintains comfort levels throughout the building.

4. Using the Calculator

Tips: Enter CFM (typically 350-400 CFM per ton of cooling) and desired velocity (typically 600-900 fpm for supply ducts). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical air velocities for different duct types?
A: Supply ducts: 600-900 fpm, Return ducts: 500-700 fpm, Low-velocity systems: 300-500 fpm.

Q2: How does duct shape affect this calculation?
A: The equation gives area - for rectangular ducts, you'll need to choose width and height that multiply to this area while maintaining proper aspect ratio.

Q3: What about static pressure considerations?
A: This is a basic calculation - actual duct design must consider pressure drop, fittings, and system effects.

Q4: How does altitude affect the calculation?
A: At higher altitudes, air density changes may require adjustments to CFM values for equivalent mass flow.

Q5: Should I round up duct sizes?
A: Yes, it's common practice to round up to the next standard duct size for practical installation.